The invention relates to a control unit, in particular a motor vehicle control unit in accordance with the precharacterizing clause of claim 1. In addition, the invention relates to a method for operating such a control unit in accordance with claim 10.
A control unit formed in accordance with the precharacterizing clause of claim 1 is already known.
It is also already known practice to design such control units such that they perform not only their actual control task but also monitoring functions for the controlled system. The program memory of a known motor vehicle control unit contains error diagnosis routines which are used to regularly check that a number of modules or components of the motor vehicle (for example sensors or actuators) are operating correctly. The test data obtained in this process are supplied to the motor vehicle control unit and are assessed there by the microprocessor (under the control of the error diagnosis routine) with regard to the occurrence of a fault in the module being monitored. If a fault is established, the microprocessor ascertains an error diagnosis result which, by way of example, indicates the type, form and instant of detection of the error. This error diagnosis result is stored in a volatile or erasable non-volatile error memory (monitoring result memory) provided for this purpose in the motor vehicle control unit. In addition, the occurrence of the fault can be notified to the driver by a warning device or the like. The motor vehicle is then taken to a workshop for repair on the basis of the warning or as part of regular servicing. In the workshop, the error memory of the motor vehicle control unit is first read by a suitable communication unit. The error diagnosis result then obtained can generally be used to ascertain the cause of the fault which has occurred or at least to narrow it down.
After a repair attempt, the error memory is reset in order to be able to establish whether the error occurs again. If this is not the case, repair has been successful. If repair is unsuccessful a number of times, i.e. the error diagnosis result occurs again, the control unit is usually sent to the manufacturer for checking with an indication of the error diagnosis result. The manufacturer checks the serviceability of the motor vehicle control unit. It is not able to reconstruct the xe2x80x9cerror historyxe2x80x9d, however, since the error memory has been erased. The manufacturer is therefore not able to check the workshop""s details regarding the error or, when there is no information, to itself ascertain the error origination history.
Besides the aforementioned possibility of error checking by implementing an error diagnosis routine in a motor vehicle control unit, it is also already known practice to make such control units xe2x80x9ccapable of learningxe2x80x9d. This is based on the control unit being delivered from the factory with fixed preset values which, however, are not able to make allowance for unavoidable component tolerances and changes to the components over their lifetime (in particular the effects of aging). Furthermore, changing environmental influences may become noticeable in operation and may result in the control parameters used not giving an optimum operating response. An adaptation routine provided in the program memory of the control unit at the factory is therefore used to regularly match the preset values and the control parameters to the actual circumstances, which means that original manufacturing tolerances and wear and tear can be allowed for and any change in the operating response on account of changing external environmental influences can be compensated for using control technology.
When the motor vehicle control unit is sent to the manufacturer for repair, the adaptively changed preset values and control parameters are also lost. These values are likewise of interest when searching for an error or when reconstructing the xe2x80x9cerror origination historyxe2x80x9d, since the discrepancies in adaptively changed values and standard values can be used to ascertain xe2x80x9canomaliesxe2x80x9d in the operating response of a module.
The invention is based on the object of providing a control unit which makes it possible to reduce costs which arise when the control unit needs to be checked at the factory. In addition, the invention aims to reduce the costs which arise when the control unit is sent to the manufacturer.
The object on which the invention is based is achieved by the features of claims 1 and 10.
The non-volatile, writable backup memory provides a storage medium in which a loss of data occurs neither when the control unit is isolated from an operating voltage supplying the control unit with power nor if the monitoring result memory is intentionally erased, for example by the workshop. The monitoring results (an individual monitoring result may also be involved) previously transferred to the non-volatile backup memory can thus be reconstructed by reading the non-volatile backup memory once the control unit has been sent to the manufacturer. Since the monitoring results contain information regarding the xe2x80x9cerror historyxe2x80x9d of the controlled system, the manufacturer now no longer has to rely on the details from the workshop in this regard. This allows it to assess the error situation simply and objectively also with regard to any rights to compensation for the workshop or for the customer.
The monitoring program routine is preferably an error diagnosis routine, with a monitoring result representing a detected error in the controlled system. As an alternative to this, the monitoring program routine may also be an adaptation routine, with a monitoring result representing a preset value and/or a control parameter used in operation by the control unit. The monitoring program routine may thus comprise both an error diagnosis routine and an adaptation routine.
Usually, a plurality of monitoring program routines are provided. This is advantageous particularly if the control unit according to the invention is controlling a system, in particular a motor vehicle, comprising a plurality of distributed modules in the manner of a central control unit, since it then becomes possible to monitor (error diagnosis/adaptation control) each individual module.
Preferably, the monitoring result stored in the monitoring result memory is in each case transferred to the non-volatile backup memory at the end of an operating cycle of the control unit. Alternatively, the monitoring result can be transferred from the monitoring result memory to the non-volatile backup memory during the operating cycle.
The non-volatile backup memory can comprise a prescribed number of N memory areas, and a current monitoring result can be transferred (possibly in part) from the monitoring result memory to the non-volatile backup memory such that if the non-volatile backup memory already holds an older monitoring result which corresponds to the current monitoring result, this older monitoring result is replaced by the current monitoring result, or that if the non-volatile backup memory holds no previously stored monitoring result which corresponds to the current monitoring result, the current monitoring result is entered into a free memory area of the non-volatile backup memory. If there is no longer any such free memory area, the oldest monitoring result stored in the non-volatile backup memory is replaced by the current monitoring result. This ensures that current monitoring results are always stored in the non-volatile backup memory, while older monitoring results can be discarded in accordance with the principle of a FIFO register only if the backup memory is filled entirely.
Further advantageous refinements of the invention are specified in the dependent claims.